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Chapter 43
The Immune System
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Learning Targets:
1. Distinguish between innate & acquired immunity
2. Name and describe four types of phagocytic cells
3. Describe the inflammation response
4. Distinguish between the following pairs of terms:
antigens and antibodies; antigen & epitope; B
lymphocytes & T lymphocytes; antibodies & B cell
receptors; primary & secondary immune
responses; humoral & cell-mediated response;
active & passive immunity
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Learning Targets:
5. Explain how B lymphocytes and T
lymphocytes recognize specific antigens
6. Explain why the antigen receptors of
lymphocytes are tested for self-reactivity
7. Describe the cellular basis for immunological
memory
8. Explain how a single antigen can provoke a
robust humoral response
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Learning Targets:
9. Describe the role of MHC in the rejection of
tissue transplants
10.Describe an allergic reaction, including the
roles of IgE, mast cells, and histamine
11.Describe some of the mechanisms that
pathogens have evolved to thwart the immune
response of their hosts
12.List strategies that can reduce the risk of HIV
transmission
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Immunity Types:
• Innate immunity: present before any exposure
to pathogens
– effective from the time of birth is nonspecific
– consists of external barriers plus internal
cellular and chemical defenses
• Acquired immunity, or adaptive immunity,
develops after exposure to agents
– a very specific response to pathogens
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
• Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
• Rapid response
ACQUIRED IMMUNITY
• Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Barrier defenses:
Skin
Mucous membranes
Secretions
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response:
Antibodies defend against
infection in body fluids.
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells.
Vertebrate Barrier Defenses
• include the skin and mucous membranes of the
respiratory, urinary, and reproductive tracts
• Mucus traps and allows for the removal of
microbes
• Many body fluids including saliva, mucus, and
tears are hostile to microbes
• The low pH of skin and the digestive system
prevents growth of microbes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
White blood cells (leukocytes)
• engulf pathogens in the body then fuses with a
lysosome to destroy the microbe
• types of phagocytic cells:
– Neutrophils engulf and destroy microbes
– Macrophages are part of the lymphatic
system and are found throughout the body
– Eosinophils discharge destructive enzymes
– Dendritic cells stimulate development of
acquired immunity
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Interstitial fluid
Adenoid
Tonsil
Blood
capillary
Lymph
nodes
Spleen
Tissue
cells
Lymphatic
vessel
Peyer’s patches
(small intestine)
Appendix
Lymphatic
vessels
Lymph
node
Masses of
defensive cells
Inflammatory Responses
• Following an injury, mast cells release
histamine, which promotes changes in blood
vessels; this is part of the inflammatory
response
• These changes increase local blood supply
and allow more phagocytes and antimicrobial
proteins to enter tissues
• Pus, a fluid rich in white blood cells, dead
microbes, and cell debris, accumulates at the
site of inflammation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Inflammatory Responses
Pathogen
Splinter
Chemical Macrophage
signals
Mast cell
Capillary
Red blood cells Phagocytic cell
Fluid
Phagocytosis
Inflammatory Responses
• Inflammation can be either local or systemic
(throughout the body)
• Fever is a systemic inflammatory response
triggered by pyrogens released by
macrophages, and toxins from pathogens
• Septic shock is a life-threatening condition
caused by an overwhelming inflammatory
response
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Natural Killer Cells
• All cells in the body (except red blood cells)
have a class 1 MHC protein on their surface
• Cancerous or infected cells no longer express
this protein; natural killer (NK) cells attack
these damaged cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Innate Immune System Evasion by Pathogens
• Some pathogens avoid destruction by
modifying their surface to prevent recognition
or by resisting breakdown following
phagocytosis
• Tuberculosis (TB) is one such disease and kills
more than a million people a year
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Acquired immunity
• White blood cells (lymphocytes) recognize
and respond to antigens, foreign molecules
• Lymphocytes that mature in the thymus are
called T cells, and those that mature in bone
marrow are called B cells
• Lymphocytes contribute to immunological
memory
• Cytokines secreted by macrophages and
dendritic cells to recruit and activate
lymphocytes
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Antigen Recognition by Lymphocytes
• An antigen is any foreign molecule to which a
lymphocyte responds
• A single B cell or T cell has about 100,000
identical antigen receptors
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Antigen Recognition by Lymphocytes
Antigenbinding
site
Antigenbinding site
Antigenbinding
site
Disulfide
bridge
C
C
Light
chain
Variable
regions
V
V
Constant
regions
C
C
Transmembrane
region
Plasma
membrane
Heavy chains
 chain
 chain
Disulfide bridge
B cell
Cytoplasm of B cell
B cell receptor
Cytoplasm of T cell
T cell
T cell receptor
T cell receptor
• Each consists of two different polypeptide
chains
• The tips of the chain form a variable (V) region;
the rest is a constant (C) region
• T cells can bind to an antigen that is free or on
the surface of a pathogen
Video: T Cell Receptors
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
T cell receptor
• The first exposure to a specific antigen
represents the primary immune response
• During this time, effector B cells called plasma
cells are generated, and T cells are activated
to their effector forms
• In the secondary immune response, memory
cells facilitate a faster, more efficient response
Animation: Role of B Cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Active Immunization
• Active immunity develops naturally in
response to an infection
• It can also develop following immunization,
also called vaccination
• In immunization, a nonpathogenic form of a
microbe or part of a microbe elicits an immune
response to an immunological memory
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Passive immunity
• Passive immunity provides immediate, shortterm protection
• It is conferred naturally when IgG crosses the
placenta from mother to fetus or when IgA
passes from mother to infant in breast milk
• It can be conferred artificially by injecting
antibodies into a nonimmune person
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Immune Rejection
• Cells transferred from one person to another
can be attacked by immune defenses
• This complicates blood transfusions or the
transplant of tissues or organs
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Blood Groups
• Antigens on red blood cells determine whether
a person has blood type A (A antigen), B (B
antigen), AB (both A and B antigens), or O
(neither antigen)
• Antibodies to nonself blood types exist in the
body
• Transfusion with incompatible blood leads to
destruction of the transfused cells
• Recipient-donor combinations can be fatal or
safe
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Tissue and Organ Transplants and MHC
molecules
• MHC molecules are different among genetically
nonidentical individuals
• Differences in MHC molecules stimulate
rejection of tissue grafts and organ transplants
• Immunosuppressive drugs facilitate
transplantation
• Lymphocytes in bone marrow transplants may
cause the donor tissue to reject the recipient
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Allergies
• Allergies are exaggerated (hypersensitive)
responses to antigens called allergens
• In localized allergies such as hay fever, IgE
antibodies produced after first exposure to an
allergen attach to receptors on mast cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Allergies
IgE
Histamine
Allergen
Granule
Mast cell
Allergies
• The next time the allergen enters the body, it
binds to mast cell–associated IgE molecules
• Mast cells release histamine and other
mediators that cause vascular changes leading
to typical allergy symptoms
• An acute allergic response can lead to
anaphylactic shock, a life-threatening reaction
that can occur within seconds of allergen
exposure
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Autoimmune Diseases
• In individuals with autoimmune diseases, the
immune system loses tolerance for self and
turns against certain molecules of the body
• Autoimmune diseases include
– systemic lupus
– rheumatoid arthritis
– diabetes mellitus
– multiple sclerosis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Exertion, Stress, and the Immune System
• Moderate exercise improves immune system
function
• Psychological stress has been shown to disrupt
hormonal, nervous, and immune systems
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Immunodeficiency Diseases
• Inborn immunodeficiency results from
hereditary or developmental defects that
prevent proper functioning of innate, humoral,
and/or cell-mediated defenses
• Acquired immunodeficiency results from
exposure to chemical and biological agents
• Acquired immunodeficiency syndrome
(AIDS) is caused by a virus
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Antigenic Variation
• Through antigenic variation, some pathogens
are able to change epitope expression and
prevent recognition
• The human influenza virus mutates rapidly, and
new flu vaccines must be made each year
• Human viruses occasionally exchange genes
with the viruses of domesticated animals
• This poses a danger as human immune
systems are unable to recognize the new viral
strain
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Latency
• Some viruses may remain in a host in an
inactive state called latency
• Herpes simplex viruses can be present in a
human host without causing symptoms
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Attack on the Immune System: HIV
• Human immunodeficiency virus (HIV) infects
helper T cells
• The loss of helper T cells impairs both the
humoral and cell-mediated immune responses
and leads to AIDS
• HIV eludes the immune system because of
antigenic variation and an ability to remain
latent while integrated into host DNA
Animation: HIV Reproductive Cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
AIDS
Helper T cell concentration
in blood (cells/mm3)
Latency
Relative antibody
concentration
800
Relative HIV
concentration
600
Helper T cell
concentration
400
200
0
0
1
2
3
4
5
6
7
8
Years after untreated infection
9
10
Attack on the Immune System: HIV
• People with AIDS are highly susceptible to
opportunistic infections and cancers that take
advantage of an immune system in collapse
• The spread of HIV is a worldwide problem
• The best approach for slowing this spread is
education about practices that transmit the
virus
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cancer and Immunity
• The frequency of certain cancers increases
when the immune response is impaired
• Two suggested explanations are
– Immune system normally suppresses
cancerous cells
– Increased inflammation increases the risk of
cancer
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Which of the following differentiates T cells and B
cells?
A) T cells but not B cells are stimulated to increase
the rate of their cell cycles.
B) Only B cells are produced from stem cells of the
bone marrow.
C) T cells but not B cells can directly attack and
destroy invading pathogens.
D) T cells but not B cells have surface markers.
E) Only B cells take part in cell-mediated immunity.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Which of the following differentiates T cells and B
cells?
A) T cells but not B cells are stimulated to increase
the rate of their cell cycles.
B) Only B cells are produced from stem cells of the
bone marrow.
C) T cells but not B cells can directly attack and
destroy invading pathogens.
D) T cells but not B cells have surface markers.
E) Only B cells take part in cell-mediated immunity.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Which of the following is not a component of an
insect's defense against infection?
A) enzyme activation of microbe-killing chemicals
B) activation of natural killer cells
C) phagocytosis by hemocytes
D) production of antimicrobial peptides
E) a protective exoskeleton
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Which of the following is not a component of an
insect's defense against infection?
A) enzyme activation of microbe-killing chemicals
B) activation of natural killer cells
C) phagocytosis by hemocytes
D) production of antimicrobial peptides
E) a protective exoskeleton
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings